The present invention relates to a semiconductor package, such as a flip chip package (FC-PKG) including a flip chip ball grid array (FC-BGA) and a method of manufacturing the semiconductor package. More specifically, the present invention relates to an inside electrode used in the semiconductor package and to a method of manufacturing the inside electrodes. It is to be noted throughout the instant specification that the inside electrodes are formed by balls and are also used in a prober for investigating a semiconductor device.
With the development of recent multimedia, a system using a silicon device tends to show high speed and high performance. However, it is becoming difficult more and more to sufficiently obtain the high performance of the device by packaging a silicon device and mounting the packaged device on a printed substrate only by a conventional method.
Specifically, even when the signal processing is carried out at a high speed, such a high-speed operation is restrained due to a delay of the signal propagation of a package and on a printed substrate and due to an error operation caused by a crosstalk noise.
Also, since the scale of LSI is increased and the performance thereof becomes higher, various difficult problems take place in the case of packaging and mounting LSI chips such that the number of I/O pins is increased. In addition, any other problems also take place such that the I/O pins become area arrays and heating from the chip is increased.
In such circumstances, the improvements of various mounting techniques are proposed as a new high-density mounting technique. As the techniques for supporting the improvements, the techniques of a chip size package (CSP) and a bear chip mount are largely developed. Particularly, in a technique of bonding a silicon chip (the chip is usually a silicon chip) to a surrounding material such as a substrate, flip chip mounting would be helpful. This is because such flip chip mounting makes it possible to reflow in a lump and to easily accomplish a desirable reliability. Moreover, there is a possibility that the flip chip mounting becomes particularly the inevitable technique in a next generation high-density package, etc.
Also, as the performance is increased and semiconductor devices are down-sized, it is required that a semiconductor package also becomes small in size and light in weight.
Herein, the flip chip mounting or connecting technique is helpful to connect a substrate and a chip in a lump by the use of protrusion electrodes (called bumps) on the chips. With this technique, it is possible to satisfy the requirements of increasing the number of pins of the I/O terminals (terminals of the inlet and outlet of circuit) and shortening the signal delayed time.
At any rate, a high-functional semiconductor device is manufactured by an electrolytic plating method, a vacuum vapor deposition method, and/or stud bump forming using a wire bonding method.
In these methods, particularly, the electrolytic plating method can simultaneously form all the bumps on a flat plane and is therefore considered to be relatively inexpensive as compared with other methods, and to be excellent in mass production.
According to recent reports about the formation of bumps, an aperture of about 100 xcexcm is plated and the plating condition is discussed on the region of the size of at least about 120 xcexcm. In addition, the content relates to mushroom-type bumps (see, Electronics Jisso Gakkai Shi (Journal of Japan Institute of Electronics Packaging), Vol. 1, No. 1, page 41, 1998).
Alternatively, recent attention has been made about a flip chip connection technique by a compressing technique. That is, the technique is a flip chip mounting technique of adhering IC to a circuit substrate by using hardening resin like film or paste and keeping the electric connection by the residual stress in the resin. This technique has a merit in that the productivity is high as compared with the prior art.
There is a technique of using an anisotropic conductive film (ACF) but since a technique of using an anisotropic conductive paste (ACP) and a non-conductive resin paste (NCP) in a driver IC of LCD, the material cost is low as compared with the case of the above-described film and a sticking device is unnecessary, the latter technique is rapidly beginning to be propagated.
The techniques are excellent in the accuracy in position-alignment and the reproducibility. However, such excellent accuracy is accomplished only on a two-dimensional package in connection with the hardness of a substrate and the relative deformation of a chip and a substrate. In other words, it is clear that such excellent accuracy can not be achieved on a high- density package of a three dimensional structure to which attention will be directed in the future. Particularly, no improvement can be achieved along the Z-axis direction in the conventional methods and, therefore, the above-described technique will be brought to a standstill.
It can be easily anticipated that the bump pitch is, at present, from 200 to 250 xcexcm, but it becomes 100 xcexcm or lower. Thus, the mounting technique practically suitable in such a case and the supply of packages thereof will be demanded. A report about the recent compression technique mentions the consideration of the damage on a substrate and a chip and also the accuracy of the warp of a substrate (see, Electronics Jisso Gijutsu (Electronics Packaging Technology), Vol. 15, No. 7, page 52,1999).
In addition, it is predicted as a future technique that the above-described three-dimensional stack type will be mainly investigated for the high-density package of a small size. Stacking bear chips might be a final form but in this case, the problems remain in the use of a semiconductor process and the protection of the chip itself. Thus, the practical use will be directed to stacking the packages, which will be accelerated.
In such a stream of the technique, proposal has been made about using micro balls as contact materials in a C4 method (Controlled Collapsed Chip Connection/Flip Chip Attach), on mounting a chip and a substrate in a flip chip technique,
In a flip chip connected CSP of prior art, a semiconductor chip is electrically connected to one surface of a wiring substrate having an electrically conductive pattern formed on the surface of a ceramic or synthetic resin substrate via micro balls called flip chip balls (FC-Ball). In this event, the connected portions between the semiconductor chip and the wiring substrate are covered with an insulating resin. On the other hand, the other surface side of the wiring substrate is mounted on one surface of a substrate or an electric part via micro balls called ball grid array balls (BGA-Ball).
Such micro balls provide an effective and reliable means for mounting, particularly, the chip and the substrate when the C4 method (Controlled Collapsed Chip Connection/Flip Chip Attach) or a technique of prior art similar to the C4 method is used.
On the other hand, Nikkei Microdevices, January, 2000, page 148, reports that a burn in inspection apparatus has been given attention as a recent technical trend of the inspecting technique in semiconductor devices. In such an apparatus also, each terminal of a probe must be certainly brought into contact with each electrode on a wafer. Otherwise, a serious problem is caused to occur. This means that such an apparatus should have a total high-accurate construction for obtaining the function as the probe, in addition to the dimensional accuracy of parts used. In particular, it is very important that alignment along the Z-axis direction must be matched between the substrate and the chip both of which are connected to each other.
Practically, it is devised that collapse of posts is utilized to absorb a variation of heights of electrodes and a spring-attached probe is used as the terminal, etc. However, a sufficient accuracy can not obtained in this probe.
Now, as the method of obtaining spherical shaped particles or grains having a uniform particle size such as the above-described micro balls, various methods are proposed. In these methods, as a method of obtaining good metal balls, a plasma rotary electrode method is said to be excellent. In the plasma rotary electrode method, the step of forming different particle sizes is also determined (Funtai Funmatu Yakin Kyokai Gaiyo Shuu (Summary of Japan Society of Powder and Powder Metallurgy), Kumagaya, et al, ""96 and ""93) and the investigation of forming uniform particle size has been carried out. Also, on the other hand, as an example of a substance having a high density, the case of copper has been investigated.
However, in the case of forming metal particles having particle sizes of not larger than 100 xcexcm, the plasma rotary electrode method makes it difficult to obtain pore-free particles. This is because the particle size distribution is widely varied to make it substantially difficult to control the particle sizes in a posterior step. In addition, the molten metal is successively released from the unmolten material in the case of melting a material (ingot). As a result, it is supposed that the heat distribution of the material portion is largely changed due to every release of the melt, whereby the possibility of generating pores is said to be large.
Also, even when metal balls having particle sizes not larger than 100 xcexcm can be formed, it is important that the size of the balls practically formed and the extent of the accuracy of the form of the metal balls can be correctly analyzed. For example, as described above, in the metal balls having the particle sizes not larger than 100 xcexcm, and more specifically of from 30 to 100 xcexcm, it is estimated to become a key to have a sufficient measurement accuracy of xc2x13 xcexcm or more. Moreover, the extents of a recess and an irregular shape can fall within 3 xcexcm at one side, but at present, the inspection/screening machine suitable for the level cannot be commercially available.
Furthermore, powdery particles applied with a soldering material, for example, applied with solder plating are considered to be considerably useful because the sufficient contact and fixing thereof are possible.
About the development of such a plating technique, a electrode electrolysis method by using a suspension of copper (Kametani, Denki Kagaku (Electrochemistry), 41, 2, page 112, 1973) and a fine particle electrolytic plating method (Takeshima, et al, Hyomen Gijitsu (Surface Technology), 41, 2, page 151, 1990) are investigated well. However, in these plating techniques, the improvement of the electric current efficiency is fundamentally and mainly considered and the properties of the plated films formed on the surfaces are not discussed.
In various plating methods, solder plating is assumed to apply to the micro balls. In this event, the solder plating has the faults that, even when the plated thickness is 5 xcexcm or thinner, the plated layer becomes a crumbling layer or the balls become non-spherical balls or an irregular shape such that they do not roll. This is because the growth rate of the plating layer is non-uniform. In addition, the micro balls are often stuck to each other like a bunch of grapes.
In order to remove the above-described faults, there is a method of forming the film with particles kept in a floated state by an impeller (a stirrer with blade) or a vibrator. However, the method is disadvantageous in that each ball becomes a non-spherical shape.
It is an object of the present invention to provide core balls which have particle sizes not larger than 100 xcexcm and which are excellent in a rolling property.
It is another object of the present invention to provide a method of manufacturing core balls as mentioned before.
Also, it is still an another object of the invention to provide composite balls made of the above-described core balls having formed on the surfaces soldering layer of a thickness of at least 20 xcexcm.
Also, it is yet another object of the invention to provide a production method of the above-described composite balls.
Furthermore, it is another object of the invention to provide a semiconductor package, which mounts a semiconductor element or chip onto a substrate by using the above-described composite balls.
Hitherto, for obtaining metal balls from fine metal particles, there is a plasma sphere-forming apparatus.
The present inventors have discovered that in the case of using the plasma sphere-forming apparatus, for obtaining spheres of large sizes, there is a considerable inferiority from the point of efficiency but for obtaining fine spheres of copper having particle sizes of not larger than 100 xcexcm, the apparatus is sufficiently effective in industrial production.
That is, the present inventors have found that the powdery particles obtained by the plasma sphere-forming apparatus are almost complete spheres, the particle size distribution is very narrow, pores are not detected in any spheres randomly selected, and even spheres having pores can be removed in the subsequent screening step, and have accomplished the present invention.
According to one aspect of the invention, there is provided a semiconductor package of a semiconductor device mounted a semiconductor element and also micro balls as electric contact points, in which the micro balls are composed of composite micro balls equipped with an electrically conductive film on the circumferences of core balls. The core balls have a sufficiently good rolling property with diameters of from 30 to 100 xcexcm. The diameter accuracy thereof is excellent. The electrically conductive film is equipped with a solder plated layer having a thickness of at least 10 xcexcm uniformly formed on the outer peripheral surface thereof is obtained. That is, in the aspect of the invention, the above-described composite micro balls are mounted to construct such that the dimensional accuracy of the Z axis of the package can be precisely controlled. In the invention, the Z axis of the package shows the axis showing the height direction to be mounted.
Also, according to the another aspect of the invention, there is provided a semiconductor package of a semiconductor device mounted a semiconductor element and also micro balls as electric contact points, in which the micro balls are composed of composite micro balls equipped with an electric conductive film on the circumferences of core balls. The core balls have a sufficiently good rolling property with diameters of from 30 to 100 xcexcm and contain at least 90% balls having the diameter accuracy of within xc2x13 xcexcm. The electrically conductive film is equipped with a solder plated layer of at least 20 xcexcm uniformly covering the circumferences of the core balls is obtained. That is, in the aspect of the invention, the composite micro balls are mounted to construct such that the dimensional accuracy of the Z axis of the package can be precisely controlled.
According to the still another aspect of the invention, there is provided a method of producing a semiconductor package of a semiconductor device mounted a semiconductor element and also micro balls as electric contact points, in which the micro balls are composed of composite micro balls equipped with an electric conductive film on the circumferences of core balls. The core balls have a sufficiently good rolling property with diameters of from 30 to 100 xcexcm. The diameter accuracy thereof is excellent. The electrically conductive film is equipped with a solder plated layer having a thickness of at least 10 xcexcm uniformly formed on the outer peripheral surface and also equipped with composite micro balls having a SnAg or SnAg-based solder plated layer formed on the core balls under a high current density of from 5 to 10 A/dm2, which results in forming a precise and stabilized plated layer to keep the Z axis at a high accuracy is obtained.
Also, according to the yet another aspect of the invention, there is provided a method of producing a semiconductor package of a semiconductor device mounted a semiconductor element and also micro balls as electric contact points, in which the micro balls are composed of composite micro balls equipped with an electric conductive film on the circumferences of core balls. The core balls have a sufficiently good rolling property with diameters of from 30 to 100 xcexcm. The diameter accuracy thereof is excellent. The electrically conductive film is equipped with a solder plated layer having a thickness of at least 10 xcexcm uniformly formed on the outer peripheral surface and equipped with composite micro balls having a PbSn or PbSn-based solder plated layer formed on the core balls under the conditions of reducing a brightener to ⅓ or lower and a low current density of at most 0.5 A/dm2, which results in forming a precise and stabilized plated layer to keep the Z axis at a high accuracy is obtained.
Also, according to a further aspect of the invention, there is provided a copper core composite micro ball assembly composed of plural micro balls connecting to the circuits of the chips of a package of a semiconductor device mounting a semiconductor element, in which each of the micro balls comprises a core ball, a first layer on a surface of the core ball, a second layer formed on the first layer, and the third layer formed on the second layer. The second layer consists of Sn. The third layer is a surface layer and consists of Ag. Herein, Ag is not more than 4% of Sn.
Also, according to the still further aspect of the invention, there is provided an inspection and selection system, which is an apparatus of selecting micro balls by inspecting the diameter accuracy of the micro balls mounted on a semiconductor package, equipped with a color tone detecting device of carrying out a color tone inspection by a camera by irradiating the micro balls with a semi-spherical illumination, a profile decision processing device of carrying out decision processing of the profile of the outer periphery by image superposing of plural times, and a sub-pixel processing device of carrying out sub-pixel processing is obtained. In this case, in the inspection and selection system of the invention, the system is constituted such that the micro balls are obtained at a measurement-guaranteed accuracy of xc2x12 xcexcm in diameter and the accuracy of the Z axis direction of a package in which the micro balls are mounted is improved.
Also, according to a yet further aspect of the invention, there is provided a copper-core composite micro ball assembly composed of plural micro balls connecting the circuit of the chip of a package of a semiconductor device mounting a semiconductor element, in which the micro balls are equipped with core balls and a solder plated layer formed on the circumferences thereof. The core balls have a sufficient rolling property with a diameter of from 30 to 100 xcexcm. The diameter accuracy thereof is excellent. The solder plated layer uniformly covers at least 10 xcexcm.
Also, according to the another aspect of the invention, there is provided a copper-core composite micro ball assembly composed of plural micro balls joining a semiconductor element to the circuit of the chip of a package of a semiconductor device mounting the semiconductor element, in which the micro balls are equipped with core balls and a solder plated layer formed on the circumferences thereof. The plural core balls each has a sufficiently good rolling property with a diameter of from 30 to 100 xcexcm and contains at least 90% the core balls having the diameter accuracy of within xc2x13 xcexcm. The solder plated layer uniformly covers the core balls at least 20 xcexcm.
Also, according to the still another aspect of the invention, there is provided a method of producing a semiconductor package for preparing a semiconductor element by applying wiring circuits to a wafer in the lump, in which micro balls are mounted before joining a substrate. At mounting a semiconductor element, a copper-core composite micro ball assembly is mounted. The copper-core composite micro ball assembly is composed of plural micro balls joining to the circuit of the chip of the package of a semiconductor device mounting the semiconductor element. The micro balls are equipped with core balls and a solder plated layer formed on the surface thereof. The core balls have a sufficient rolling property with a diameter of from 30 to 100 xcexcm. The diameter accuracy thereof is excellent, and the solder plated layer is uniformly covered at least 10 xcexcm.
Also, according to the yet another aspect of the invention, there is provided a method of producing a semiconductor package for preparing a semiconductor element by applying wiring circuits to a wafer in the lump, in which micro balls are mounted before joining a substrate. At mounting a semiconductor element, a copper-core composite micro ball assembly is mounted. The copper-core composite micro ball assembly is composed of plural micro balls joining to the circuit of the chip of the package of a semiconductor device mounted a semiconductor element. The micro balls are equipped with core balls and a solder plated layer formed on the surface thereof. The core balls have a sufficient rolling property with a diameter of from 30 to 100 xcexcm and contain at lease 90% the core balls having the diameter accuracy thereof of within xc2x13 xcexcm. The solder plated layer uniformly covers the core balls at a thickness of at least 20 xcexcm.